Lens apparatus and image-pickup apparatus

ABSTRACT

Provided is a lens apparatus mounted to a camera including an image-pickup element, including: a focus lens means movable in an optical axis direction for focusing; a zoom lens unit; a zoom detector for detecting a zoom value of the zoom lens unit; an aperture-stop device; a stop-value detector; a splitting optical unit; a focus-condition detection unit; an actuator; a controller for controlling the actuator based on an output from the focus-condition detection unit; and a manual operation member, wherein the controller obtains an F-number of the lens apparatus based on outputs from the zoom detector and stop-value detector and when the F-number exceeds a predetermined value, the controller causes the actuator to stop the focus lens unit and switches to a condition in which the focus lens unit is driven by the manual operation member.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of application Ser. No. 11/690,352,filed Mar. 23, 2007, the entire disclosure of which is herebyincorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a lens apparatus including a splittingoptical unit disposed on an optical path of an image-pickup opticalsystem, for performing automatic focus based on a light beam from thesplitting optical unit, and to an image-pickup apparatus including thelens apparatus.

2. Description of the Related Art

Up to now, various automatic focus techniques for an image-takingapparatus such as a still camera or a video camera have been proposed.For example, Japanese Patent Application Laid-Open No. H09-274130discloses a lens and image-pickup apparatus in which a splitting opticalunit is disposed on an optical path thereof and a focus-conditiondetector based on phase-difference detection is disposed on a splitoptical path from the splitting optical unit.

According to the still camera, after performing the automatic focuscontrol while an aperture stop is opened, a light quantity is adjustedby stopping down by the aperture stop, and then shooting can beperformed. On the other hand, taking moving picture for broadcast,video, or cinema is constantly in a shooting state, so the automaticfocus control is demanded under any stop state.

In the case of shooting a moving picture, a dividing optical unit isdisposed on an image side of the aperture stop and phase-differencedetection is performed based on a light beam obtained by division. Insuch a case, when stopped down to a value smaller than a thresholdvalue, because, for example, a subject is bright, a pupil of a secondaryimaging lens is vignetted. As a result, a phase difference cannot bedetected accurately, so automatic focus precision deteriorates to causea malfunction.

When stopped down more, the pupil of the secondary imaging lens may becompletely vignetted, so the phase difference cannot be detected toperform the automatic focus control.

When a dividing optical unit is provided on an object side of anaperture stop as in the first Embodiment disclosed in Japanese PatentApplication Laid-Open No. H09-274130, the above-mentioned problems donot occur. However, a size of the entire optical system increases.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a small andlight-weight lens apparatus capable of switching between automatic focuscontrols at a time of the shooting with stop-down and performing theshooting depending on an intention of a photographer, and animage-pickup apparatus including the lens apparatus.

According to a first aspect of the present invention, the presentinvention provides a lens apparatus for mounting on a camera includingan image-pickup element, which comprises a focus lens unit which ismovable in an optical axis direction for focusing; a zoom lens unitwhich is movable in the optical axis direction for zooming; a zoomdetector for detecting a zoom value of the zoom lens unit; anaperture-stop device in which an aperture which can change in size toadjust a light quantity; a stop-value detector for detecting a stopvalue of the aperture-stop device; a splitting optical unit disposedbetween the aperture-stop device and the image-pickup element; afocus-condition detection unit for detecting a focus condition based onlight from the splitting optical unit; an actuator for driving the focuslens unit in the optical axis direction; a controller for controllingthe actuator based on an output from the focus-condition detection unit;and a manual operation member for moving the focus lens unit in theoptical axis direction by a manual operation, wherein: the controller isconfigured to obtain an F-number of the lens apparatus based on anoutput from the zoom detector and an output from the stop-valuedetector; and when the F-number, adjustable by the stop value of theaperture stop device, exceeds a predetermined value, the controllercauses the actuator to stop movement of the focus lens unit and switchesto a condition in which the focus lens unit can be driven by the manualoperation member.

Further features of the present invention will become apparent from thefollowing description of exemplary embodiments with reference to theattached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a structural diagram illustrating a first Embodiment of thepresent invention.

FIG. 2 is an optical structural diagram illustrating a focus-conditiondetector.

FIG. 3 is an optical path diagram illustrating a state where an aperturestop is stopped down so that a stop value exceeds a threshold value ofan F-number.

FIG. 4 is an optical path diagram illustrating a state where theaperture stop is further stopped down so that the stop value exceeds thethreshold value of the F-number.

FIG. 5 is a flowchart illustrating an operation in a first Embodiment ofthe present invention.

FIG. 6 is a structural diagram illustrating a second Embodiment of thepresent invention.

FIG. 7 is a flowchart illustrating an operation in a second Embodimentof the present invention.

FIG. 8 is a structural diagram illustrating a third Embodiment of thepresent invention.

FIG. 9 is a flowchart illustrating an operation in a third Embodiment ofthe present invention.

FIG. 10 is a structural diagram illustrating a fourth Embodiment of thepresent invention.

FIG. 11 is a structural diagram illustrating a fifth Embodiment of thepresent invention.

DESCRIPTION OF THE EMBODIMENTS

Hereinafter, embodiments of the present invention will be described indetail with reference to the attached drawings.

A phase-difference detection system in the embodiments includes aprimary imaging lens for imaging a split light beam, a field lensdisposed close to an expected imaging plane of the primary imaging lens,and a secondary imaging optical system disposed in the rear of the fieldlens. According to such a system, a set of object images are formedbased on light beams passing through different portions of the pupil ofan imaging optical system. Each of the object images is detected by aphotoelectric conversion element array disposed in the rear of thesecondary imaging optical system. A phase difference is detected by afocus-detection apparatus for determining a focus condition of theimaging optical system based on a relative deviation amount between theobject images.

First Embodiment

FIG. 1 is a structural diagram illustrating a lens apparatus and acamera according to a first Embodiment.

As illustrated in FIG. 1, a lens apparatus 30 includes a focus movablelens unit 1, a magnification movable lens unit 2, an aperture stopdevice 3, a splitting optical unit 4, and a relay lens unit 5, which aredisposed along an optical axis. A camera 40 includes an image-pickupelement 6.

The magnification movable lens unit 2 includes a magnification variator2 a and a compensator 2 b for compensating for an image plane variationcaused by magnification. A focus-condition detector 7 is disposed in adivision direction of the splitting optical unit 4. An output of thefocus-condition detector 7 is connected with a CPU 8. An output of azoom detector 9 of the magnification adjustment lens unit 2 is connectedwith the CPU 8. In addition, respective outputs of the CPU 8 areconnected with a focus actuator 11 and an aperture-stop control circuit12 in order to drive the focus movable lens unit 1 and the aperture-stopdevice 3. The aperture-stop control circuit 12 detects a stop value ofthe aperture-stop device 3 and outputs the detected stop value to theCPU 8. A manual operation member 13 is manually operated to move thefocus movable lens unit 1 manually.

The focus-condition detector 7 outputs, to the CPU 8, a focus detectionvalue obtained based on a light beam split by the splitting optical unit4. The CPU 8 performs calculation based on the focus detection value andcauses the focus actuator 11 to move the focus movable lens unit 1 inthe optical axis direction. Therefore, automatic focus control isperformed.

The CPU 8 has an associated memory (not shown) which is used to storeone or more programs for running on the CPU 8. In other embodiments, thefunctions of the CPU 8 may be performed by an integrated circuit, logicchip, or the like, which are configured to carry out the steps of theprogram.

In order to perform light-quantity adjustment, the aperture-stop device3 is driven by the CPU 8 through the aperture-stop control circuit 12based on a luminance signal of the image-pickup element 6.

FIG. 2 is an optical structural diagram illustrating the focus-conditiondetector 7. As illustrated in FIG. 2, a primary imaging lens 7 a, afield stop 7 b, a field lens 7 c, an aperture stop 7 d including twoaperture portions are disposed on the optical axis in the divisiondirection of the splitting optical unit 4 through the aperture-stopdevice 3. A set of light-receiving element arrays 7 f and 7 f′ aredisposed in light exit directions of the two aperture portions of theaperture stop 7 d through a set of secondary imaging lenses 7 e and 7e′. The field stop 7 b and the field lens 7 c are provided on anexpected imaging plane of the primary imaging lens 7 a.

The field lens 7 c has a function of imaging light beams passing throughthe aperture stop 7 d and the secondary imaging lenses 7 e and 7 e′ ontwo regions disposed symmetrical with each other with respect to theoptical axis of the primary imaging lens 7 a. The light beams that havepassed through the respective regions generate light-quantitydistributions on the light receiving element arrays 7 f and 7 f′.Outputs of the light receiving element arrays 7 f and 7 f′ are sent tothe CPU 8.

In the focus-condition detector 7 illustrated in FIG. 2, when an imagingpoint of the primary imaging lens 7 a is located on the front side ofthe expected imaging plane, light-quantity distributions related toobject images formed on the two light-receiving element arrays 7 f and 7f′ are close to each other. When the imaging point of the primaryimaging lens 7 a is located on the rear side of the expected imagingplane, light-quantity distributions generated on the two light receivingelement arrays 7 f and 7 f′ are separated from each other.

A deviation amount between the light-quantity distributions generated onthe two light receiving element arrays 7 f and 7 f′ has a functionalrelation with a focus deviation amount of the primary imaging lens 7 a.When the deviation amount is calculated by the CPU 8, the focusdeviation of the primary imaging lens 7 a, that is, a focus deviationdirection and a focus deviation amount of the imaging optical system canbe detected.

Assume that an F-number of an optical system from the focus movable lensunit 1 to the image-pickup element 6, which corresponds to a minimumstop diameter of the aperture-stop device 3 including two regions, is athreshold value F1. The F-number is expressed by f/D where f denotes afocal length of the optical system and D denotes an entrance pupildiameter. In the case of the focus-condition detector 7 including two ormore sets of secondary imaging lenses, the threshold value F1 iscalculated based on two regions provided on the aperture-stop device 3,which correspond to the secondary imaging lenses 7 e and 7 e′ having ashortest base length.

As illustrated in FIG. 3, when the aperture-stop device 3 is stoppeddown such that a stop value exceeds the threshold value F1 of theF-number, a light beam passing through the aperture stop 7 d isvignetted. Therefore, the barycenter of each of the light-quantitydistributions generated on the two light receiving element arrays 7 fand 7 f′ is displaced, so an accurate deviation amount between thelight-quantity distributions cannot be measured. When the light quantityreduces to increase a storage time or to lower an S/N ratio, an accuratefocus condition cannot be detected.

As illustrated in FIG. 4, when the aperture-stop device 3 is furtherstopped down, the light beams do not reach the two light receivingelement arrays 7 f and 7 f′, so the focus condition cannot be detected.

Therefore, in this embodiment, the adjustment of the aperture-stopdevice 3 and the automatic focus control are performed based on theflowchart illustrated in FIG. 5. When the aperture-stop device 3 isstopped down such that the stop value exceeds the threshold value F1(=F/8) of the F-number to increase the numeral value of the F-number,the operation of the focus actuator 11 is suspended by the CPU 8 inresponse to the output of the focus-condition detector 7 to stop themovement of the focus movable lens unit 1 in the optical axis direction(automatic focus). Then, the focus movable lens unit 1 is switched to amanual operation condition (manual focus condition) by the manualoperation member 13. An alarm indicating that the focus movable lensunit 1 is switched to the manual focus condition is displayed on adisplay device (not illustrated) of the camera 40. When the F-number issmaller than the threshold value F1, the automatic focus controlcontinues or the operation returns to the automatic focus control.

In order to prevent a reduction in resolution of a video picture, it ispreferable to control the threshold value F1 of the F-number in a rangein which an Airy disk diameter does not exceed a pixel pitch of theimage-pickup element 6. Therefore, it is desirable to ensure theautomatic focus control in this range. Thus, it is desirable that thethreshold value F1 satisfies the following expression where λ denotes acenter wavelength of a wavelength range in which the image-pickupelement 6 has sensitivity and P denotes the pixel pitch of theimage-pickup element 6.

1.22·λ·F1/P>1  (1)

In this embodiment, for example, ⅔ type CCD is used as the image-pickupelement 6. An image screen size is 9.6 mm in a lateral direction and 5.4mm in a longitudinal direction. The number of pixels is 1920 in thelateral direction and 1080 in the longitudinal direction. The pixelpitch P is 0.005 mm. The use wavelength range is 400 nm to 700 nm. Thecenter wavelength λ is 550 nm (=5.5·10⁻⁴ mm). Therefore, the left sideof the expression (1) is calculated as shown in the followingexpression. Thus, it is apparent that the condition of the expression(1) is satisfied.

1.22·5.5·10⁻⁴·8/0.005=1.0736  (2)

Second Embodiment

FIG. 6 is a structural diagram illustrating a lens apparatus and acamera according to a second Embodiment. In FIG. 6, the same portions asthose illustrated in FIG. 1 are expressed by the same reference symbols.In this embodiment, a second light-quantity-adjusting member 21 which isan ND filter is disposed on an optical axis between the splittingoptical unit 4 and the relay-lens unit 5, unlike the first Embodimentdescribed with reference to FIG. 1. The second light-quantity-adjustingmember (ND filter) 21 can be inserted into or removed from the opticalpath by an actuator 22 driven in response to a command from the CPU 8.The second light-quantity-adjusting member 21 has an effect of reducinga light quantity for the image-pickup element 6 to ¼ which correspondsto 2 in stop value. An F-number F2 in the case where the ND filter isinserted is set by the following expression.

F2=F1/2  (3)

In the second Embodiment, there are two light-quantity-adjustment modes.In a first light-quantity-adjustment mode, as same as in the firstEmbodiment, the automatic focus and the manual focus are switchedtherebetween based on the F-number according to the operationalflowchart illustrated in FIG. 5.

In a second light-quantity-adjustment mode, the aperture-stop device 3is controlled according to a flowchart illustrated in FIG. 7 such thatthe stop value does not exceed the threshold value F1 of the F-number.The second light-quantity-adjusting member 21 is inserted into theoptical path in order to continue the automatic focus control. When theF-number becomes equal to or smaller than F2, the secondlight-quantity-adjusting member 21 is automatically removed from theoptical path.

Third Embodiment

FIG. 8 is a structural diagram illustrating a lens apparatus and acamera according to a third Embodiment. In FIG. 8, the same portions asthose in the above-mentioned embodiments are expressed by the samereference symbols. In the third Embodiment, continuous light-quantityadjustment can be performed using a second light-quantity-adjustingmember 23 by an actuator 24, unlike the second Embodiment described withreference to FIG. 6. For example, a physical stop or a graduation NDfilter is used as the second light-quantity-adjusting member 23.

Also in the third Embodiment, there are two light-quantity-adjustmentmodes. In a first light-quantity-adjustment mode, as in the firstEmbodiment, the automatic focus and the manual focus are switchedtherebetween based on the F-number according to the operationalflowchart illustrated in FIG. 5.

In a second light-quantity-adjustment mode, the aperture-stop device 3is controlled according to a flowchart illustrated in FIG. 9. That is,when a light quantity of a subject increases and the F-number reachesthe threshold value F1, light-quantity adjustment is switched to becarried out by the second light-quantity-adjusting member 23 and theautomatic focus control continues while the aperture-stop device 3 isheld at the threshold value F1. When a light control amount adjusted bythe second light-quantity-adjusting member 23 becomes zero, theoperation returns to the light-quantity adjustment using theaperture-stop device 3.

Fourth Embodiment

FIG. 10 is a structural diagram illustrating an image-pickup apparatusincluding a lens apparatus and a camera according to a fourthEmbodiment. In FIG. 10, the lens apparatus 30 is mounted on the camera40.

The image-pickup element 6 is disposed in the camera 40. A secondlight-quantity-adjusting member 25 which is an ND filter is disposed infront of the image-pickup element 6. The second light-quantity-adjustingmember 25 is driven so as to be inserted into or removed from theoptical path by an actuator 26. A luminance signal of the image-pickupelement 6 is output to the CPU 8 through a second CPU 27 forlight-quantity adjustment. The second light-quantity-adjusting member 25has an effect of reducing a light quantity to ¼ which corresponds to 2in stop value. The F-number F2 is set to F1/2.

In the fourth Embodiment, there are two light-quantity-adjustment modes.In a first light-quantity-adjustment mode, as in the first Embodiment,the automatic focus and the manual focus are switched therebetween basedon the F-number adjusted by the aperture-stop device 3 according to theoperational flowchart illustrated in FIG. 5. In a secondlight-quantity-adjustment mode, the aperture-stop device 3 is controlledaccording to the flowchart illustrated in FIG. 7 such that the stopvalue does not exceed the threshold value F1 of the F-number. Byinserting second light-quantity-adjusting member 25 into the opticalpath, the light quantity is adjusted by the second CPU 27 based on theoutput of the image-pickup element 6. When the F-number becomes smallerthan F2, the second light-quantity-adjusting member 25 is automaticallyremoved from the optical path.

Fifth Embodiment

FIG. 11 is a structural diagram illustrating an image-pickup apparatusincluding a lens apparatus and a camera according to a fifth Embodiment.In the fifth Embodiment, a second light-quantity-adjusting member 28 isa shutter adjustment aperture stop. continuous light-quantity adjustmentcan be performed using the second light-quantity-adjusting member 28 byan actuator 29.

In the fifth Embodiment, there are two light-quantity-adjustment modes.In a first light-quantity-adjustment mode, as in the first Embodiment,the automatic focus and the manual focus are switched therebetween basedon the F-number adjusted by the aperture-stop device 3 according to theflowchart illustrated in FIG. 5.

In a second light-quantity-adjustment mode, the aperture-stop device 3is controlled according to the flowchart illustrated in FIG. 9. When alight quantity of a subject increases and the F-number reaches thethreshold value F1, the F-number adjusted by the aperture-stop device 3is held to the threshold value F1. Then, the operation of the actuator29 is controlled by the second CPU 27 to control a shutter speed of thesecond light-quantity-adjusting member 28, thereby adjusting the lightquantity. When a light control amount adjusted by the secondlight-quantity-adjusting member 28 becomes zero, the operation returnsto the light-quantity adjustment using the aperture-stop device 3.

In the fifth Embodiment, the shutter adjustment aperture-stop is used asthe second light-quantity-adjusting member 28. However, if a variable NDfilter is used or a camera gain is adjusted, the same effect isobtained.

While the present invention has been described with reference toexemplary embodiments, it is to be understood that the invention is notlimited to the disclosed exemplary embodiments. The scope of thefollowing claims is to be accorded the broadest interpretation so as toencompass all such modifications and equivalent structures andfunctions.

According to the embodiments, the automatic focus control at the time ofstop-down for image taking can be performed depending on the intentionof a photographer, and reductions in size and weight can be realized.

This application claims the benefit of Japanese Patent Application No.2006-094122, filed Mar. 30, 2006, which is hereby incorporated byreference herein in its entirety.

1. A lens apparatus, comprising a focus lens unit, wherein the lensapparatus includes a first focusing mode in which the focus lens unitmoves based on an output from a focus-condition detector which detects afocus condition and a second focusing mode in which the focus lens unitmoves by a manual operation, and wherein in a condition where anF-number exceeds a predetermined value, the first focusing mode isprohibited and the second focusing mode is executed.
 2. An apparatusaccording to claim 1, including a splitting optical unit which spits thelight beam to be shot which has traveled through the focus lens, whereinthe focus-condition detector detects the focus condition by using thelight beam split by the splitting optical unit.
 3. An apparatusaccording to claim 1, further comprising: a zoom lens unit disposed on areduction side of the focus lens unit; an aperture-stop disposed on areduction side of the zoom lens unit; a splitting optical unit disposedon a reduction side of the aperture-stop; a focus-condition detectorwhich detects the focus condition by using the light beam split by thesplitting optical unit; and a CPU which determine whether an F-numberwhich depends on the zoom lens unit and the aperture-stop exceeds thepredetermined value or not.
 4. A camera, comprising: an image pickupelement; and a lens apparatus which guides a light beam to be shot froman object to the image pickup element, wherein the lens apparatusincludes a first focusing mode in which the focus lens unit moves basedon an output from a focus-condition detector which detects a focuscondition and a second focusing mode in which the focus lens unit movesby a manual operation, and wherein in a condition where an F-numberexceeds a predetermined value, the first focusing mode is prohibited andthe second focusing mode is executed.
 5. A method of controlling a lensapparatus which includes a first focusing mode in which a focus lensunit moves based on an output from a focus-condition detector whichdetects a focus condition and a second focusing mode in which the focuslens unit moves by a manual operation, the method including the stepsof: determining whether an F-number of the lens apparatus exceeds apredetermined value or not; and prohibiting the first focusing mode andexecuting second focusing mode in a case the F-number exceeds thepredetermined value.